Many kinds of instruments are known of the class generally called X-Y plotters. Such instruments record electrical analog data on charts, such as ordinary graph paper sheets .Iadd.(popularly known as "cut-sheets" or "cut-charts").Iaddend., by means of a pen, a heated stylus, or other known marking means. With respect to the recording medium, the deflection of the pen or stylus in the horizontal or X-direction is a function of one electrical input signal, and the deflection in the Y-direction, perpendicular thereto, is a function of another electrical input signal. With the input signals derived from suitable transducers, such instruments are used for example to record curves of strain vs. stress, or pressure vs. temperature.
In a typical instrument of this class, potentiometers or other transducers are linked mechanically to the pen-driving means, and their outputs compared with the input signals at the input terminals of servo amplifiers. These amplifiers in turn drive servo motors which operate to position the pen in the X and Y directions.
Such instruments are often complex and costly. Many lack convenient means for plotting families of curves without drawing superfluous lines on the chart, incident to changing gain or zero settings or to removing and replacing the chart on the machine. Many, moreover, lack means to replace a chart on the machine accurately in the same position, so that zero controls must be manipulated after the chart is again in place; this again draws unnecessary lines on the chart. Many prior instruments require special chart paper with edge perforations; the present invention does not.